IT'S the news we all feared – putting on just a few pounds of fat can increase the risk of suffering a heart attack by nearly a fifth.

A study of almost 200,000 people has shown that a one-unit increase in body-mass index, which measures body fat levels, raises the risk of heart failure by 17pc.

Until now, scientists suspected but could not be certain that extra body fat raised the chances of suffering heart disease.

For someone measuring 5ft 10in, one BMI unit is equivalent to 7lb, while for someone who is 5ft 4in tall it is the same as putting on 6lb.

The findings provide fresh evidence that obesity can cause heart disease, according to the researchers.

They also found an increase in body fat raised the risk of diabetes by 35pc for every BMI unit.

"We knew already that obesity and cardiovascular disease often occur together," said Dr Tove Fall, a researcher at Uppsala University in Sweden, who led the study with researchers at Imperial College London and the University of Oxford.

"However, it has been hard to determine whether increased BMI as such is dangerous. In this study we found that individuals with gene variants that lead to increased body-mass index also had an increased risk of heart failure and diabetes.

"The risk of developing diabetes was greater than was previously thought."

The study, published in the journal PLOS Medicine, looked at FTO, a gene related to obesity that regulates appetite, in 198,502 people from around Europe.

They found that the more copies of a defective variant of the FTO gene a person had, the higher their BMI was and the greater the risk of heart disease.

Tam Fry, spokesman for Britain's National Obesity Forum and chairman of the Child Growth Foundation, described the findings as "very important".

He said: "What is really exciting is they have pinned down causality, which is essential when coming up with any pronouncement like this.